package com.zjz.listener;

import javax.servlet.ServletContext;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

//统计网站在线人数：统计session
public class OnlineCountListener implements HttpSessionListener {


    //创建session的监听：看你的一举一动
    //一旦你创建一个session就会触发一次这个事件！
    @Override
    public void sessionCreated(HttpSessionEvent se) {
        ServletContext ctx = se.getSession().getServletContext();

        System.out.println(se.getSession().getId());
        Integer onlineCount = (Integer) ctx.getAttribute("OnlineCount");
        if(onlineCount == null){
            onlineCount = new Integer(1);
        }else {
            int count = onlineCount.intValue();
            onlineCount = new Integer(count+1);
        }

        ctx.setAttribute("OnlineCount",onlineCount);

    }


    //销毁session的监听，看你的一举一动
    //一旦session销毁就会触发一次这个事件！
    @Override
    public void sessionDestroyed(HttpSessionEvent se) {

        ServletContext ctx = se.getSession().getServletContext();
        Integer onlineCount = (Integer) ctx.getAttribute("OnlineCount");
        if(onlineCount == null){
            onlineCount = new Integer(0);
        }else {
            int count = onlineCount.intValue();
            onlineCount = new Integer(count-1);
        }

        ctx.setAttribute("OnlineCount",onlineCount);

    }


}



